The present invention relates to a chuck. More particularly this invention concerns a lever-action lathe chuck with replaceable jaw inserts.
A standard lever-action chuck for use in a lathe or the like has a body adapted to be rotated about a chuck axis. A plurality of angularly equispaced guides are pivotal in the body about respective guide axes extending secantally of the axis, that is about axes that are offset from the chuck axis and that each lie in a plane generally perpendicular to the chuck axis. Respective elongated jaw arms axially slidable in the guides each have an outer end to which is fixed a jaw insert intended to directly engage a workpiece being gripped by the chuck. Means is provided to axially displace the jaw arms between outer positions with their outer ends spaced forward from an end face of the chuck body and inner positions with their outer ends close to or even recessed in the end face of the chuck body. Further means is provided for pivoting the jaw arms about the respective secantal guide axes so that, in the outer position, the outer arm ends can pivot in to grip a workpiece.
Such chucks are typically used in axially confronting pairs to rotate a workpiece such as a crank shaft that is gripped at both ends and rotated about the coaxial chuck axes to machine bearing and crank surfaces of the crankshaft. The retractability of the jaw arms makes it possible to load the workpiece into the chucks and remove it from them radially of the machining axis without having to axially displace the chucks. The pivotability of the jaw arms makes it possible to clasp them on the workpiece without applying an axial force to the workpiece, which force could distort it.
Such a chuck is clamped very solidly to the workpiece and it is fairly common for the jaw inserts to shift slightly relative to the arms, no matter how solidly these steel parts are bolted together. This axial shifting of these inserts can put an axial stress on the workpiece, potentially deforming it.
It is therefore an object of the present invention to provide an improved lever-type chuck with removable jaw inserts.
Another object is the provision of such an improved lever-type chuck with removable jaw inserts which overcomes the above-given disadvantages, that is whose jaw inserts will remain in position no matter how hard the chuck is clamped on a work piece.
A chuck has according to the invention a chuck body adapted to be rotated about a chuck axis and a plurality of elongated jaw arms angularly spaced about the axis, pivotal in the chuck body about respective guide axes extending secantally of the chuck axis, and axially slidable in the body. Each jaw arm has a front outer end formed with a generally axially extending and radially inwardly directed outer face and an axially outwardly and forwardly directed inner face extending radially inward from an axially inner end of the outer face. Each outer face converges axially outward with the chuck axis and forms a small acute angle with the chuck axis. Respective jaw inserts each have a pair of faces complementary to and flatly engaging the respective jaw faces. These inserts are releasably secured to the jaw outer ends with the insert faces bearing on the jaw faces.
Thus with this system the jaw inserts are extremely solidly mounted on the respective arms. The radially outwardly directed forces exerted on the jaw inserts when they are pressed radially inward against a workpiece will merely serve to press them into better contact with the jaw faces they already engage, so that they will not shift at all. Nothing short of compression or deformation of the steel arm or jaw insert, which is impossible under normal conditions, can move the jaw insert on its arm.
The faces according to the invention are planar. In addition each insert is formed with at least one throughgoing hole extending substantially parallel to the outer insert face. A screw fastener in the hole has a head bearing on the insert and a shank threaded into the outer end of the respective jaw arm.
Each jaw has an inner gripping face extending generally parallel to the chuck axis. In addition each inner face extends at substantially 90xc2x0 to the respective outer face. Each jaw has a flat front face diverging radially inward away from the respective inner face.